The longer this covid situation drags on, the more it's looking like an 8 game 2020 season, if we get one at all. Each team plays each of the other teams once, then playoffs, then Grey Cup.
Working backwards from the date of the Grey Cup, November 22nd, that puts week one of the 9 week season on the Labour Day weekend. I'm assuming the bare minimum one bye week per team, necessary due to having an odd number of teams in the league. If the playoffs consist of just 1 vs 2 divisional championships then Grey Cup, no divisional semis, the season could start as late as the September 11th & 12th weekend. It may even be necessary to just have the divisional regular season winners as the Grey Cup teams, no other playoffs.
If the teams are going to have a bit of a training camp before the season, it may be necessary to forego the Labour Day games this year. It's quite possible that there will be no preseason games this year , just going straight into the season out of training camp. Maybe do a controlled scrim with the nearest other franchise in the league. They might play one pre-season game on the Labour Day weekend, but that's it. Due to the odd number of teams in the league, one team might not even get to play a scrim/pre-season game. Maybe the teams could carry camp size rosters for the first couple of weeks of the season, then cut down to the regular 46 players in week 3. I hope Touchdown Atlantic still happens, and if it does, it should be as soon as possible in September.
The absolute last, "drop dead" date to decide whether or not there will be a 2020 CFL season, then, is August 15th. That gives all the coaches, players, and team staff two weeks to get travel plans in order, notice to other employment they may have, and so on. There are already a couple of jurisdictions in Canada that have banned large public gatherings until August 31st. If those bans get extended into September, then I'm afraid there won't be a 2020 CFL season at all.