Hwy 401 can be a "bit of a bear" at times, we live north of Toronto and try to avoid it when we can. Can't speak about LA freeways but transiting Dallas/Fort Worth is a piece of cake compared to the 401.
An alternative is the 407 ETR, a toll road that parallels the 401 to the north. It's expensive, could cost $50CDN or more one way to get across. They have agreements with most states so you will probably get a bill (don't know what happens if you don't pay it, here we can't renew our plates if we don't pay).
Diesel is about the same cost as it is here in California taking the exchange in.
You may want to look at campsites early, the parks get busy in the summer in Ontario, most provincial parks are fully booked in advance. Upper Canada Village is a nice historic stop east around the Kingston area.