I just joined, and saw that no one answered your post. I ride this bike trail frequently and it's excellent. It runs through farm fields, along the Missisquoi River, 26 miles from St. Albans to Richford. At St. Albans, you can park your car at the start, pick up a free guide and map, and go. Look for the bike nailed to a post about 10 feet in the air, at an intersection with Rt. 105 on the north end of St. Albans. There are also other places to park along the trail. My favorite is at The Abbey Restaurant in North Sheldon.
The surface is nice, but noisy under the tires. Maximum grade 3%. The crushed granite is easy to ride on and stable. There are 14 road crossings of Route 105 from St. Albans to Richford, so take care with these. The trail is well maintained, although the ATVers have kicked up stones on a portion near Richford. I don't recommend this trail for narrow tires just because of an occasional stone.
Have you tried the Burlington bike path and Colchester connection? The Burlington path runs from the south end of Burlington, across a brand new bridge over the Winooski River, through Colchester, and out onto a 3 mile causeway across the lake to the Lake Champlain islands. This month only, on weekends, Local Motion is running a ferry across the single gap in the line, a 200 ft. cut in the causeway for boat access. Once you cross the gap, you can bike all through the islands and up into Canada.
I've never crossed into Canada on a bike, but I expect it's like any other crossing: have some good ID (e.g., driver's license). Most people in southern Quebec stick to French, but you can get by OK.