Is there a Canadian Tire nearby? Napa?
Transaxle: Any GL-5 or GL-4 gear oil in the 75-90/80-90 range will work, no problem. Some oils give better shifting. When I switched to Redline MT90, there was a noticeable improvement in shifting. All Renault transaxles leak; some a little, some a lot. Sounds dumb to say it but the one thing they won't tolerate is no oil. Check your transaxle level regularly until you get a handle on how often it needs topping up. Check it at least once at the start of the season and before any long drives.
Engine: It is a classic "flat-tappet" engine and it does benefit from a bit more phosphorous/zinc than you find in most modern oils. Again any oil is better than no oil. Mobil 1 5W50 is usually available at auto parts stores. It has a reasonably level of phosphorous/zinc. Failing that, motorcycle shops are another source of phosphorous/zinc rich oils -- albeit, not cheap. See what the local shops have and do a bit of research. I would stick with oils that have a 50 at the top like 5/10/15/20 - 50. I used Mobil 1 V-Twin oil 20W-50 for a long time. It was perfect and Canadian Tire carried it. But, it doesn't seem to be available anywhere in Canada anymore.
Diesel oils are controversial. Lots of people are using them but, there is always a but, they have additives to suit issues that diesel engines have, not the gasoline engine issues. Some people are quite concerned, some not at all.
Temper it all with the fact that 90% of modern oils are far better than 90% of what was available in the 60s!
The oil filters are standard Ford filters (3/4" 16 tpi thread). You want the really short one. Just ask for a filter for a 1980 Renault 5 and you'll be good. You can also fit a 90° adapter and then fit regular length Ford filters. Not a big deal though as usually pampered cars, like Europas, get twice as many, or more, oil changes than they actually need.