Is this a big detour route? or does it take about the same time as going on the 410?
The highway 7 route versus the 401 might add an hour to two hours to your trip, depending on traffic and road conditions. Highway 7 is a 2 lane highway, so if you get stuck behind a truck or RV, it could be slow going.
If you are only going for a couple days to Montreal, then I would probably just power right through on the 401 and get to Montreal ASAP. Unless you are going to take some time to see Ottawa or Kingston along the way, there isn't really much point in taking a detour.
If you take the 401 and are an Avril Lavinge fan, you can stop in Napanee and see where she grew up.