I think that answer to your first question is yes, provided that you're exercising the priviliges from your UK PPL. It all depends a bit on how you want to move forward, as the main reason for keeping accurate track of your experience is to be able to prove that you have that experience at a later stage. So, if you are looking to upgrade to another licence or add a rating that requires a certain amount of experience, at that point you will need to be able to show the paperwork that shows that experience.
I only have one licence, so perhaps I'm not the best person to answer this, but I can see both options working out:
1. You could use two logbooks, logging whatever you fly on your UK licence in one, any flights using your Canadian licence in the other. You could perhaps cross-credit something at a later stage and this would make sorting through the various flights easier at that point.
2. You could log everything in one logbook, but you would need to switch between the different rules for every flight as you switch using the two licences. If you ever need to show a certain amount of experience, it can get a bit complicated if you need to add up the accumulated hours on one licence only.
Alternatively, you could consider going down the electronic route. I know that a lot of the e-logbook applications allow you to run two or more logbooks side by side. It might make things easier.