Why not the tailgate of your truck? From ground, you squat, keep back straight, grab side grab handles/pack strap loops and use your legs to lift to tailgate, then slip in.

In woods, you have bow of canoe, rocks/logs. Anything you can use to lessen the strain of bringing a heavy pack from it's lowest position.

Facing the pack straps, lifting with them and setting the pack on one knee, then inserting your arm of choice is far easier than bulling it up from the ground with most of the strain on your arms/upper-body, lower back if your not lifting with your legs.
I can and will take it up that way, if there's no alternative but I avoid it if I can. Your beating yourself up when you don't really need too.

80 lbs is way more than I would want for my pack. Are you 2x portaging with pack 1x and canoe separate, or are you 1x portaging?  I'd consider heavy food pack, and a gear pack with the canoe, changing that when the food pack lightens up.

If your buddy is bigger and stronger than you and can't muscle your pack the way you do tells me that you do have a technique that works for you, but it doesn't necessarily mean it's a technique that's good for your body ;)

The Voyagers carried loads that most of us couldn't even get off the ground. They also had short life expectancies and I would bet spine/hip problems that probably left them in chronic pain after their tripping days :'(

You said the Isle Royale trip really put the hurt on your body? Imagine what 2 weeks or longer will do in the WCPP?
I have to think it will be much more strenuous and if your body revolts on you, where will that leave you :'(

On a solo trip the heavier the load, the greater chance of injury, whether from the weight or a inadvertent slip/fall.
I understand detesting someone/ something helping you, but like the old Bible proverb says, Pride really does go before a Fall. Or as my Dad use to tell me, " Learn to work smarter, not harder "  ;)