Michael Cera is not the right choice for Nick. Nick does not wear his puppy-dogginess on his face so obviously. Also, Trish should be more oblivious and less actively nasty.
Norah's pretty good, and the rest of the gang--Nick's friends, Norah's friend, all the random club kids--are fabulous.
But Nick is just wrong. He's not THAT insecure.
Edited to add verdict: the book was WAY better. Less pat, more realistic, more passionate.