Why doesn’t he play in Canada, sharpen his skills...and then return?
Because with the larger field, the deeper end zones, and the separation between offensive and defensive lines football in Canada is even more of a passing game than in the U.S. Passing is not Tebow's strong suit.
Because his deficiencies as a quarterback (primarily throwing accuracy) could actually be magnified in the CFL. Since they have one less down, passing accuracy is probably the most important thing for a QB in that league.
He should absolutely do that. He loves the game. Play it. I played college football as a 5’10” 175 pound “monster” back on defense 45 years ago at a Division II school. I loved every minute of it and have never regretted playing even though it was not at the level I wanted to be at.
Right now the CFL season is more than half over. Not saying it is impossible but it would be difficult for him to join at this point. US players do take some time to adjust to the different rules.