My husband, myself, and our two kids are planning on moving to Canada in a little more than 18 months from now. I am Canadian, have lived in the USA for 15 years, my husband is German, and my kids are of course Canadian, American and German (though currently working on getting all that paperwork in order). My husband will be keeping his current job and working remotely, and I have been a SAHM for the past several years.
When would you file if this was your timeline?
Apply as soon as you have your application in order, even if it's early. It will likely be completed before the time you have set in 2022.
The only downsides to this approach are very minor - first, when his application is approved it will come with an expiry date, typically twelve months after medical. He'll have to travel to Canada, 'land', and then he's a PR with right to work - but there is no requirement to immediately reside full-time in Canada (he could return the next day basically). Obviously travelling to Canada to do the formalities is not a big deal from USA so travelling within that expiry date shouldn't be difficult.
Related minor downside: if he doesn't reside immediately in Canada, it will reduce his flexibility on the residency obligation (two years of any five year period) by the amount of time he stays outside of Canada before settling permanently.
Note, I've completely ignored any covid-related travel restrictions and the like such as isolation on arrival - too far in the future to guess or worry about what they may be at the relevant time.
Ah - one important thing, as Canadian citizen residing abroad you will have to demonstrate your intent to return to Canada to live. It's in the guide. That's most likely the only challenging thing about your application, as you won't need to sponsor your children, etc.