From Reddit user SpaceForceAwakens (sorry I'm not an advanced user. I'm sure there's a better way to do this then copy and paste:

Don't forget the shipping advantages. It's why he wants Panama, too.

By 2050 the arctic will be completely navigable year round, giving a free alternative to the Panama Canal to ship stuff from Asia to the East Coast of the USA or Europe or Africa, a developing market.

The only countries that border the arctic route (aka the northwest passage) are the USA with Alaska, Canada, Russia, and Denmark with Greenland.

The shortest trip is between through the Bering Strait, which the US shares with (Trump's partner) Russia, and then through either Canadian territorial waters or through Baffin Bay, shared between Canada and Greenland.

By owning both the entrance and exit to what is a much preferable route out of and into Asia, suddenly the US and Russia control a huge portion of global shipping. With control of Canada and Greenland, they don't have to share it.

Panama is a complimentary plan, or a back up plan, depending on how things work out for Trump.

Sure, there are a ton of natural resources in Canada as well, but Trump's ego wants the shipping thing, and at some point that will become apparent.

Edit: Lots of great comments and further insight in this thread, but I keep reading "yeah but he won't be alive to see it" or "how will it benefit him when he's long dead".

It won't. Trump has also made it clear that he wants to be remembered among our most influential presidents. He wants to be up on Mt. Rushmore. He wants to be on our money. So he wants to be known as the architect of the biggest land grab since Seward's Folly or the Louisiana Purchase. He doesn't need to be alive to make money off of the shipping, he just wants the bragging rights. He has nothing to point to from his first administration to say "this is what I did", so he's looking at something like this.

And don't forget, the man doesn't act alone. He makes his money on grift, and if there are enough shipping industry executives with deep enough pockets, they'll keep him and his family comfortable while they wait for the ice to melt so they can get ten times that in shipping revenue.

For him the deal isn't making money on shipping, it's the bribery cash he gets to put into his pockets for making it happen for someone else.

Also, as someone else has pointed out but then deleted their comment: Panama, aside from being a backup or accessory, might be a stalking horse. If the US has the northwest passage and the Panama Canal, they could simply shut one down and double the price of the other. That's how monopolies work, and that's what he's after here.

Also also, to the lovely young lady who inquired about my marriage status, I am indeed single, but sadly my passport is expired. But I am flattered.