Although I have never ridden all the way to Kitchener, I have come close.

First get an Advermap Recreational Trails map for the area. It's called Map 2 Golden Horseshoe. If you can't find them at a bike shop try the Ontario Travel Centre at Dundas and Yonge. That map shows the trails. I would not consider riding on the over-crowded highways in this region, especially if you are going slow with an inexperienced rider. Sadly Google maps only show roads for cars and don't indicate narrow or dangerous routes.

The basic route I recommend is taking the Waterfront trail to Hamilton. From there take the Hamilton Brantford Trail Trail. It's kind of hard to find from downtown Hamilton. From Brantford take the Paris rail trail then connect with the Cambridge Paris trail. The latter I have not been on so I don't know if it is bike friendly. Perhaps another member can tell you.

At your pace give yourself 2 days to get there assuming you are not going to rush. Camping is not great as there are almost no campsites on the trail. Stealth camping is not something you do with a partner. There are however great and inexpensive accommodation almost everywhere along the way. This route is partly off-road and except for the end bit, I have been on it many times. If you are interested in more detailed info please email me through this forum.