Offhand I can’t find where I’d read that Ron Perlman had auditioned for Riker, but both he and Frakes got their big roles at the same time (never having really seen North and South I can’t speak to that).
But that’s not as important as this http://en.memory-alpha.org/wiki/Performers_considered_for_Star_Trek_roles if you scroll to TMP you’ll see that both Lance Henriksen and ANDREW ROBINSON auditioned for Decker!
