I'm assuming he wants programming in English? If so your options are limited, most of the streaming lineups geoblock those outside the US.

Until recently I used a service called USTVNow with my Roku, and it worked fantastic and was super easy to use, but for some reason Roku shut them down. You can actually still get it if you run a Plex Server by installing a user channel, but I think we're getting out of bounds for both you and him there.

Netflix and Amazon, in addition to geoblocking US content, actively block VPN connections if they can figure out that you're on one. That said, Netflix Mexico has a pretty good lineup of programming, almost all of which is available in English, and Amazon's catalogue is slowly growing but mostly consists of Amazon Originals at this point.

I've never tried the firestick with Kodi. It's illegal to stream content that you would normally pay for, so I tend to stay away from that sort of thing. It may however work well here, and chances of getting prosecuted for it in Mexico are fairly slim.