If a greencard holder got deported from the u.s. after they committed a serious crime to belize but one day wanted to travel from belize to africa or saudi arabia, would they be allowed a layover flight in canada or not assuming theyve never set foot on canadian soil?? Can someone please tell me. Thanks.

You asked the same question on Flyer Talk and received a lot of very knowledgable response. They gave you all the links to rules/regulations. Answer hunting here won't get you a 'better' result.

As several of the FT'ers explained, you likely cannot transit through either Canada or the US. Look for flights via Mexico or someplace in South America