It's extremely likely to pass. Since this isn't technically a "treaty", Congress can only pass a bill to disapprove of it [1]. Obama can then veto the disapproval, and there are enough Democrats to override the veto.
Congress must pass a bill to revoke the US sanctions, which is a separate act of legislation from assenting to this deal. There are several Executive Orders which Obama can revoke but the embargo proper is embedded in US legislation.
