Really well-executed game, the theme fits and the atmosphere/story is really funny :D
It's also a 'blast' to play and it feels great to see enemies fly off into the sky after a good hit!

Small things:

• Hitboxes should probably be more generous, having the blast radius of the shot also hit/affect the enemies
• Cannon should maybe have a trajectory line for the start point of the shot, that then fades the further away you are trying to shoot
• Enemy train should give feedback then hit (Visually or via. audio)
• Your trains smoke gets in the way visually while trying to shoot
• Maybe have a top bar for total distance traveled in comparison to the end goal

Great game, keep it up!