Secure and deterministic MACs which are not strongly secure?
A deterministic MAC can use canonical verification, but it doesn't have to.
Thus, the question allows you to create deterministic MAC without canonical verification. How can you use this to your advantage?

Hint 1: 


   What if you add some auxiliary (constant) bit to the output of the  tagging algorithm of $\Pi$. How can you define the verification algorithm of $\Pi'$ to still be UF-CMA secure but not SUF-CMA secure?


Hint 2:   


   This question is very similar to another question given here: Difference between INT-CTXT and INT-PTXT