There lots and lots of opportunities for hiking in the areas you're talking about. (Quite a few for paddling, as well, of course.)
If you have some time, making a trip along the Kancamagus Highway through the White Mountains of New Hampshire is good for a day or possibly two. There are a number of pull-offs with hikes varying from a brief walk to several miles. (Sabbaday Falls is a very nice and very short one). Most of the pull-offs are suitable for an RV, but a handful (all clearly signed) are not. The road itself is fine for any RV.
There are several Vermont state parks grouped around the Groton State Forest, which are interconnected by a nice network of hiking trails, generally not overly strenuous. Further west, Mt Mansfield and Camel's Hump, among other mountains, have a number of trails up and down and fabulous views from the top if the weather is cooperative. If tackling Mt Mansfield, do not attempt to take your RV through Smuggler's Notch. It's a really neat road, but very tight and twisty between rocks at the top and most years a few semi trucks (which are banned with good reason) or RVs (which are not technically banned, but still must obey the laws physics) get physically stuck there.
If you have time, spending a day or week or two in the Adirondacks would be very appealing. There are some very pretty roads and hikes and lakes there.