Perhaps I could offer a partial answer to your question. I was involved in drafting the Ontario regs.
Yes, there's quite a bit of difference among the regulations in the different provinces. To give you a striking example, the Quebec regulation calls for a flush sample; you let your water run for five minutes, and the probability of finding a high level of lead is very low. On the other hand, Ontario has a 30-minute type of stagnation, which brings out a higher number.
It should be said that there's a lot of discrepancy among the ones that follow Health Canada's guidance, Ontario regulations, or Quebec regulations, and some provinces have very little enforcement of any kind. Yes, there is a lack of common regulations, or even common goals, in reducing lead across Canada.