That your B1/B2 visa is valid for 10 years doesn't mean that it entitles you to stay in the US for 10 years -- it just means that you're allowed to show up at the border at some time within the validity period and ask to be let in.
If you're allowed entry, the amount of time you can stay legally in the US will be determined by the immigration officer at the time and documented on your (possibly electronic) Form I-94. Usually you will get a limit of 6 months from your date of entry.
Going to Canada and back again will generally not give you a new period; instead the expiry date of your previous I-94 will be carried over to the one issued when you reenter from Canada.
However if you are a legal permanent resident of Canada, this may not hold for you. The rules are somewhat open to interpretation, though -- what is formally the case is that a "short" visit to Canada will not reset your clock. Supposedly it not is considered a "short" visit when you're actually going home, but this doesn't seem to be set in stone and it's conceivable that the immigration officer will still consider it a short visit if you're merely going home for Christmas and then back again.
In principle it is also possible to apply for an extension of stay once you're in the US. See here. There's a $290 filing fee, and it doesn't seem to be easily predictable whether the application will succeed.