Last time we traveled through Ontario from Niagara Falls to Sarnia (2009) we spent a long time in Canadian Customs in Niagara Falls. They went through the motorhome from one end to the other. We plan to be out east this summer and will NOT be going through Canada on the way back west, even though it is shorter.
We are no hurry so will travel NY 5 from Buffalo to the OH state line, then jump on I-90 to west of Cleveland, then OH 2 west to Toledo. We have traveled that route before (since we avoid the toll roads) and it is definitely longer and slower - - but that's our choice. It may or may not be yours. Just our 2 cents.