Yeah, if you have BTC balance at the time of the fork on Coinbase then your account will automatically be credited with an equal balance of B2X. Coinbase will support buys, sells, sends, and receives for both BTC and B2X. Services for both chains may be disabled several hours before and 24-48 hours after the fork.
At the time of Bitcoin Cash fork, Coinbase didn't support it, but I guess now almost all Coinbase users would be keeping their funds on Coinbase to get quick access to B2X.
If B2X has the same valuation as Bitcoin then you double your money, otherwise no.