RV'ing in Canada - where can you stay to get facilities?

Based on my experience doing 2 RV trips of 2/3 weeks length in Australia and Canada:

Where you're allowed to stay varies from place to place - in national/provincial parks you're definitely only allowed to stay at designated campsites (and there is a difference between "day" campsites and sites where you can stay overnight). The same is true inside towns. In the true "outback" (i.e. thinly populated areas where few tourists go) nobody cares even when there may be official rules. But note that RV rental companies typically only allow you to drive on paved roads.

What you need depends on the capabilities of the RV - the larger ones can be fully self-sufficient for a few days. In ours, the limiting factor was the "gray water" tank from the sink and shower. In smaller RVs, the limiting factors are lack of toilet and shower, and possibly the fridge (if it runs on a battery rather than propane).

As for where to get water, electricity and emptying tanks - campsites, definitely. Many will let you use their dump site for a small fee without having to stay there.

Honestly, I'd plan on staying at a camp site most or all nights. It's just nicer to have a a real toilet and shower rather than the cramped facilities of an RV. And if you're traveling alone or with only 1 or 2 other people, that allows you to take a small RV (van conversion) without such facilities and save a lot on rental fees and gas - more than the campsites cost.

As well as the regular RV parks, a number of box stores in Canada will allow you to park for free. Walmart is well-known for this, but their official policy is that it is at the discretion of the individual stores. Some municipalities have been cracking down on this by forcing the stores to have permits.