Definitely not. The Tappan Zee Bridge isn't open to bicycles, nor would you want to ride it if it were. You're only two Hudson crossings are the GW and Bear Mtn Bridges, roughly 45 miles apart, which is why the Bear mtn ride is always a century.

You had asked for hills, which is why I suggester the train to Peeksville, then you could ride to Bear Mtn, and come down the west side back to the GW. That can be a nice ride for you, but once you cross the river and start south, you're committed to completing the ride.

This is why I like using Metro North. I can rail past the close-in burbs, do a nice loop, and have plenty of choices for where to end, going longer if I wish, or bailing to the nearest station if necessary.