Is it legal to exceed the Advisory Speed Limit in Canada?
Yes, it's legal to ignore it. However, if you do and cause an accident, you're at fault.
An advisory sign gives advance notice of conditions on or adjacent to a highway that are potentially hazardous to traffic. A driver may choose whether or not to follow the suggestion given by the sign. Ignoring the advice is not an offence in itself, but anything that happens because the signs are not given consideration may be an offence.
An upcoming condition requires most vehicles to slow.
That's what the sign is saying. You, as Pilot-In-Charge, get to examine the roadway, situation and conditions to determine whether another speed is appropriate, within the white-sign posted limits. This may be LESS than the yellow-sign limits!
I hardly need to tell you what to do with good sightlines on a clear dry day with a Lotus Formula 3. Tee hee!
However, it's perfectly possible in adverse conditions for even the advisory speed to be too fast. If you're in marginal icing conditions with a curve on a bridge, then yeah. So really, the number on the sign is barely useful: the valuable information is authorities thought it was worth C$500 to put it there.
The government has done their part by warning you of the deviant condition, now it's all on you.
That is also why they generally don't have an "End advisory speed zone" - this should be obvious to the competent driver. If it isn't obvious, that means you can't see well enough to ascertain that - so caution remains called for.
Violating the sign isn't an infraction of its own. If you drive a speed below the speed limit and even below the advisory speed, and yet still have an accident related to speed, you will probably be guilty of "careless driving" in the form of "too fast for conditions". Some jurisdictions break those out as separate infractions.
So in that sense, you violated the sign, even if you literally conformed with the sign.
But if you make it through safely, without offending the sensibilities of an observing officer, you're fine.
E.g. British Columbia law here, see 144 and 146 permitting authorities to set speed limits and link to document specifying how regulatory limits must be signed in order to have force of law. It is difficult to prove a negative but note that the canonical list of regulatory signs does not include a yellow speed sign. See also advisory/warning signs: ours is at page 23.
Looking at both, you may catch that every regulatory sign is white* and every advisory/warning sign is yellow. This is a USA/Canada standard.
* Except for stop/yield, which have entirely unique shapes not reused for other signs. Or night driving signs which are standard black/white inverted (rather clever UI really).
Traffic related laws are provincial in Canada. It is probably more productive to ask legal questions at the law stackexchange.
This 2016 Globe and Mail article corresponded with the transportation ministries of various provinces in Canada.
Their finding was that it is legal to exceed advisory speed signs -- commonly found at curves that lead onto or out of main highways.
Contrary to the accepted answer, there is no warning of "at fault" or not based on the correspondences with transportation ministry spokespersons
The explanation from some transportation ministry spokespersons strongly suggest that the advisory speeds ultimately correspond to a certain lateral G your vehicle may experience at the curve -- that would be why angle and curvature need to be considered.
Contrary to some other answers, it would be unreasonable to think the advisory speed is a strict safety limit, easily affected by weather conditions, for all cars. Vehicles have very different handling characteristics. While lightly loaded passenger cars with new tires may take 0.9G before skidding (same as breaking), a truck may roll over ever at the same G even if skidding does not occur. It would be extremely hazardous to post advisory speeds as safety limits only for small passenger cars, which would cause confusion and accidents for large trucks. On the same token then, it is unreasonable to think an advisory sign compatible with all traffic on the road would be the strict safety limit for passenger cars.
What should you do in practice?
That depends on your vehicle. Assuming a regular passenger car, a good way to use the sign is to follow it strictly at interceptions that you have not driven to before or in large vehicles or in vehicles whose handling you are uncertain of. As you develop familiarity with a certain area, you can apply a certain ratio to the advised as long as you are driving the same car (same tire, same load). With passenger cars, your ratio is likely above 1. (With trucks, often below!)
I know my car is safe driving at ~1.5x the advisory speed in the highway exits/entrances I usually drive in; on regular road with sharp turns, there is no uniform ratio, so just x1. That is, at those speeds, I don't need to worry about needing to break due to curvature and thus don't need to worry about whether there is another vehicle behind me. It doesn't mean I should max out the skidding limit of my tires at all times, which would be silly. It means I wouldn't worry about skidding as long as I am well below the ratio I know. If I drive to a new area, however, just in case the implicit G is not strictly equal, I would more closely follow the advised speed. If there is another vehicle closely behind me, I would also follow the advised speed -- that way we both slow down; I know I don't need to break due to road curvature and they don't have to react. If I haven't changed tires for a long time, I would reduce the ratio.