I just rode to Montreal and back this weekend. Slabbed it all the way, what a boring ride! (I just had to get there and back quickly, scenic route was not an option). Coming back on the Sunday night, I got bogged down with cottage country traffic merging on 401 West at Peterborough and Lindsay (which actually made things more "interesting" trying to get thru this). If you can, go the scenic route, either hwy 2 along the lakeshore/river, or hwy 7 to Ottawa and hwy 148 in Quebec.
Side note: as soon as you hit the Ontario/Quebec border on 401 (turning into hwy 20 in Quebec), roadwork begins in Quebec, non-stop all the way to Montreal, and in a lot of places in Montreal as well. Makes for big traffic messes all over. Depending on your final destination, allow some time to deal with this.