That certainly sounds like a tough trip!
This is not a personal recommendation, because I certainly have not traveled that route (and I suspect the number of people that have done that in an EV are very few!), but one tool I would use in this case is Plugshare's trip planner. This will allow you to set a route and it will show you charging stops along the way, and allow you to filter by nearby amenities, although for much of that trip, I am guessing you are going to have to take what you get. Looks like one particular challenge is from Slave Lake, AB to Fort Vermilion, AB, which looks to be 407km (249 miles). Even without elevation and weather to take into account, this is going to be pushing it in the Model 3. But even worse is that the two stations at either end of that gap are 100kW Flo CCS units which unless you've done the DIY upgrade to your 2018 to support CCS are not going to be helpful to you.
Possibly a more feasible option would be to divert (I guess it's not an awful diversion) through Peace River, AB and charge up at the ChargePoint L2 there, and then make your way to the Best Western Plus Mirage Hotel & Resort in High Level, AB, which has a Tesla destination charger and is a mere 300km between those points (and would probably make a decent overnight stopover point.
Past that point you will definitely be relying on no more than level 2 and outlets, and there are slim pickins' at that.