Through upstate NY to Maine

One point on US 20: there is a low RR bridge on 20 in eastern NY. Check your RV height and prepare for an alternate go around of that area.

Following the Seaway Trail along Lake Ontario is an interesting way to cross NY. There are many state parks along the trail, many on the lake that are good overnight stops. One of my favorites is a bit south of the trail, but well worth a stop - Letchworth State Park. Three beautiful waterfalls; the park is often sited as NY's finest. If you take the Seaway Trail, wave as you pass through Oswego!

US 11 is the fastest 2 lane across northern NY, but NY 3 through the Adirondacks is more interesting. A bit windy, but a pretty drive. As a side trip, the Adirondack Museum is worth a stop. Taking either US 11 or NY 3, you will pick up US 2 as you cross into Vermont.

I've taken US 2 all the way to Lamoine State Park in Maine (just outside Acadia National Park). Lots of small towns & villages; you won't make great time like you would on the interstates, but it is a lot more enjoyable.

For a different route back, I've taken US 20 across MA & NY. Again, lots of small hills & small towns, but more interesting than the MA Turnpike & NY Thruway, which parallels it.

A must see on your trip is Web City. Defiantly don't miss that.

Sounds like a reasonable route going out. Route 2 is a nice enough road. For the section between Burlington and Barre/Montpelier where it parallels I-89, I would suggest taking the Intestate as it's generally a little nicer and quicker and the scenery is hardly different. (For a good bit of that distance the two roads are separated by a Jersey barrier or not much more.)

I would consider a detour through the New Hampshire white mountains. There are a few different roads through there, and all are generally good roads and beautiful. My favorite is probably the Kancamagus Highway. The Conway/North Conway area on the eastern side is usually pretty slow going and crowded (it's quite a commercial strip, lots of outlet stores and so forth...which is either exciting or dreadful, depending on your temperament).

The Fairbanks Museum in St Johnsbury, VT is worth a visit in my opinion. It's a very traditional, mostly natural history museum, which hasn't changed a whole lot in many decades. In some ways it's as much a museum museum as a natural history museum. Down the road a bit the Athenaeum (public library) has a fantastic little art gallery. Both of these institutions owe a lot to Mr Faribanks and the success of his scale manufacturing many years ago.

Another museum that's only a little out of the way is the Shelburne museum in Shelburne, VT. This is a very eclectic museum, a quite large and spread out space, and I'd suggest devoting a whole day to seeing it. Not too far is the Lake Champlain Maritime Museum which has good reports, as well.

If you have certain sorts of activities or sites you're particularly interested in, or certain sorts of campgrounds you prefer, it would be helpful to know for making relevant suggestions. The Vermont state parks are generally well-kept and well-run but the campgrounds are fairly primitive--no hookups, dirt roads, often many fairly small (but private) sites, etc. The NY state parks I've been in have been quite decent, too, and tend to have slightly more modern campgrounds.

another way which I have taken a few times is Buffalo hwy 20 to Seneca Falls then 81 to Watertown then 3 to Saranac and lake Placid then to Lake Champlain. lots of scenery.

We are not going into Canada. Just skirt along the border on hwys. 37 and 11 if they are decent roads.

If you plan going from Niagara falls east in Canada be aware of the freeway in Toronto.

plan your trip so no rush hour driving through Toronto Metro area. There are times it is a headache of the most severe kind

We crossed Lake Champlain on the ferry from Plattsburgh NY to Grand Isle. We stayed at Apple Island RV Resort. There is also a state park there. We drove across Hwy 2 to Bangor. Stop at Cabot Cheese factory and Ben & Jerry's Ice Cream factory. On the way back, don't miss Acadia National Park in Bar Harbor. We stayed at The Narrows Too RV Resort. Shuttle (free) stops at RV park. Expensive but they have different rates depending if you want to be on the wtaer. Stop at Quechee Valley KOA and visit Quechee Gorge. If you want to go more south, we like Ives Run COE campground in Tioga PA. (make reservations). We also liked Hickories City Park in Owego NY. In Bradford PA the Zippo Lighter and Case Knives factory and museum.

Take the ferry to Grand Isle to get to RT 2, it's fun and inexpensive.