To find places, I've had success with finding places via http://www.bbcanada.com. Despite the "90s" look of the website, the information does seem to be accurate, up-to-date, and with more smaller places listed than anywhere else I've looked.
To find objective reviews, given the small size of B&Bs and their low volume of business compared to traditional hotels, I doubt there is a centralized objective source - you'll have to look at several things, such as:
- The CAA has lists of recommended hotels (e.g. see http://www.caasco.com/Auto/Road-Trip ), it may include some smaller places
- Sites like bbcanada.com have some reviews, but they tend to be biased to the positive side ("testimonials" from happy customers, not reviews)
- Booking.com reviews
- Some places may even have ratings on Yelp, Google+, etc.
- Perhaps local chambers of commerce, city hall websites, tourism board websites, etc have recommendations?
Also, hotels/B&Bs that have a highway sign (see http://www.mtc.gov.on.ca/en/tourism/tods.shtml ) must meet certain quality standards before being allowed a sign, so this may be an indication as well. However, as far as I know these criteria have more to do with "playing well within the tourism industry" than your actual guest experience.