is it possible to have a round trip to this bridge from canada to u.s and from u.s. to canada if i have nexus card?

It's absolutely YES

The bridge is nexus only, and requires toll money on the nexus card or the use of an ez pass type cashless payment. All occupants must have a nexus card, and the bridge serves traffic to both countries.

Yes

You can, need Nexus and EZPass or cash

Not sure, best to phone the office direct