I don't think it's as simple as replacing a few words in the Acts of Parliament. If we remove the Monarch as head of state, what is it replaced by? For a comparison, take any other republic, and examine how they constrain what a President can do.
There's 1000 things that deserve more attention than changing something which has absolutely no negative effect on the day-to-day lives of Canadians. That ambivalence though would turn quickly to polemics as monarchists and republicans took up sides, and every other group you can think of fought to shape the "New and Improved Canada" to suit their fancy.
Coke switched back to the old formula...turns out change isn't always a good thing, despite what the infomercials may have told you.