Law vs Shanks will be no different from Kid vs Shanks.
Shanks has Future Sight, he can see everything Law attempts to try.
Also, Law can't move Shanks nor Cut Shanks with ROOM, Haki is too strong.
I can see it going exactly the same way Shanks vs Kidd did realistically.
Shanks will see whatever strong attack Law is going to use, realize he has to take him seriously. Hell, he might know about how powerful the ope ope is thanks to his government connections.
Law got lucky he got matched up against a cocky guy like Teach who is sloppy, probably his best matchup among top tiers(and he still lost
)