Will the Arris SB8200 work with xfinity 2gig plan?

The SB8200 is not compatible with Gigabit internet service. Comcast/Xfinity rates it for wired download speeds "up to 957, 936, or 935 Mbps" depending on the device version. It isn't compatible with their "enhanced" upload speeds either.

Follow the "See all modems" link near the bottom of https://www.xfinity.com/support/internet/customerowned, and then under the "Compatible Modems" heading click the Arris list. Using devices on Internet speed tiers for which they are not compatible with tends to produce unexpected results, often speeds well below the plan speeds you are paying for. 

AFAIK Comcast/Xfinity has never said how they provision devices operating on speed tiers they're not compatible with. All I can tell you is that many customers who tried it have reported that they don't get full speed. There's a tendency to think the device will operate at the maximum speed it is capable of, but that doesn't seem to be the case. Instead, incompatible devices often seem to be provisioned to run at speeds well below what they should be capable of.