Is the Rhode Island class considered cannon, given that it’s only appearance is in an alternative future?
also, are there any stats for it?
According to Memory Alpha, the USS Rhode Island is a (refit) Nova Class Starship. The class of that name in Star Trek Online would be, strictly speaking, Beta-Canon.
There are no explicit stats for the ships that I know of, but you can simply take the Nova spaceframe of the Core Rulebeook as basis and refit your way into the Rhode Island Class of about 2400 (or whenever your game takes place), using standard refit rules in the chapter “Starship Creation”. 
Mister X has the right of it, but as a reminder, there are no stats for the Constitution Refit, just use the stats for the original and add refits as allowed. After a certain time period, the refit also gives it the ‘face lift’ Same with the Soyuz class I imagine, which is just a Miranda class with ‘sensor pods’ glued on to the side.
In my Trek reality the Rhode Island is a Saber-class patrol corvette, built on the same spaceframe as the Nova, but intended for border patrol and escort duty.
However, on screen, it was intended to be Nova.
It’s a descendant of the Nova class.