Hi Tonia - as a commonwealth citizen you will be able to acquire visas on arrival for Kenya, TZ and Uganda. Provided you have evidence of further travel and are not displaying evidence that you wish to settle in Rwanda you should be able to get a visa at the border. Not sure if Rwanda has an embassy in Canada, if not make some inquiries in Nairobi. The only difference may be that you will have to pay more for the visa in NBO than at the border (cost of running the embassy get added on).
On other point - at the moment the east african 3 (Kenya, TZ and Uganda) allow you to travel to each country and back without getting a new entry visa, however if you leave the group and go to Rwanda its is possible that you may need to get a new entry visa. (To explain if you arrive in Kenya - NBO and then travel to Tanzania, Rwanda and Uganda and finally back to Kenya - then Kenya may require a new entry visa. If you are only going to be in Kenya for the purpose of flying back home you should be able to get a transit visa - its about half the cost of a full visa.)
Hope this helps.