I have a couple of bags that came with a canoe I bought. Curious if anyone knows how they work - is there a pump or some such thing I need to fill them? Tried blowing but that was a fail…the couplings on the tubes seem sealed. I am probably being an idiot.
Interested to see if they are junk or if they hold air…..

Might need some new valves.

Did you unscrew the mouthpieces? The little ridged smaller-diameter piece screws out to inflate, in to seal.

Belated thanks for the advice. As it turns out, the 'nipples' on those red plastic pieces at the end of the tubes pull out, opening the valve and allowing one to inflate by mouth.

After huffing and puffing & passing out for a while, I came to with both bags fully inflated.

Letting them sit overnight to see if they hold air or if they leak. I'd be surprised if they both are intact in the morning.

The follow-on question: are they intended to be inflated by mouth? Or is there some kind of a hand pump that goes with these things?

I put a air nozzle on a hose to my "pancake" air compressor and first inflate it through the air release valve, then finish blowing it up through the airbag's inflation hose with the air nozzle.

No passing out this way. There are also large volume hand-pumps and 12-volt pumps available.

I hope they hold air. Patching is possible but it is a bear just finding the leaks and getting a good patch on them.

I've owned bags like those.
Although I own a large volume hand pump (sort of like a large tire pump), I usually filled them at home with my shop vac. Put the hose on the vac's discharge and it fills quickly.

Keep in mind that you'll need to monitor the pressure in those bags.
Heat (or cold) will effect ho "full" they are. Too full can actually pop a bag. You might fill them to the "perfect" pressure during a cool morning or in the shade and then load the boat onto your car, or launch onto the water. Extreme increases in temps can greatly expand the pressure in those bags. Parking in a blazing hot asphalt lot for even a half hour will make those bags seem like they may explode.

Conversely, if you leave them unfilled or semi filled and drive 70 mph on the interstate, the bags can flop in the highway breeze. That's not very good for them either Give them just enough air to keep them firm but not too firm.

The hose with the red valve is great for leaving a little air out, or adding a little more if needed.

And treat them with 303 a couple times per season and they'll last longer.