Congratulations on being invited to speak at the conference - woohoo (quietly)
I've been several times to the New England area, it's a beautiful part of the country.
I once flew into Toronto, never again! I had to do Canadian customs/immigration on landing, walk down a corridor to get my Boston flight then do US customs/immigration, a real pain when you're tired, hot & feeling very hassled. Can't recommend that way to get to US. Can recommend "upgrading" on Virgin, better seats, better food/drinks, better baggage allowance.
If you mean Bethel, Maine I drove there from western Mass some years ago. Took my time lots of trees. Lots. Many places just to stop & look. Got roadside motels no prob, one did put me in mind of Psycho though!
North Conway NH is worth a visit good scenery & retail therapy for those who require it, some sort of tax concession in NH; no purchase tax or some such. Mount Washington also worth a visit, don't miss the cog railway.
Niagara is best viewed from the Canadian side , worth the trip but customs, immigration again. The town is very commercial these days but worth a day trip. Welland canal worth a look too.
I always went into NY City by bus, Greyhound, convenient & just something different. When flying from JFK I did it (the City) on my way home, there was left luggage (secure) at the bus depot & I could then get a bus or taxi to the airport. You would probably need to check the left luggage situation it may have changed after 9/11.
It's generally considered cheaper to book the hire car from UK, I always used Alamo & found then very good. I was spoiled really as mostly my pal, in Mass, would lend me his car for the duration. I would not contemplate driving in downtown NY. If you go there see if you can find the garment district, I got some great deals on winter clothes one time; when I said I would be over my allowance the guy offered to buy the coat I was wearing!
Hope this helps, enjoy.
HH