Filling gas tank issue

Couple things to try. First, use a borescope and look down the filler neck and make sure there are no obstructions. The most common cause of the pump shutting off is a leaf or something stuck in the fill neck and it causes the fuel to back up the tube.

Next is the vent tubes of the fuel tank and fill neck to the canister are clogged. Or the canister itself is full of fuel. If this is the case then when you fill the tank the fuel creates a seal and the vapor cannot be vented to the atmosphere so it has to be routed the to ORVR system described in the attachments.

I would remove this and blow air through the lines and then check the canister by shaking it to see if it has fuel in it.

Let me know if you have questions. Thanks

If it is the canister, all I have to do is shake the gas out of it and put it back in place or do I have to replace the canister?

Unfortunately no. Once they get fuel in them the charcoal breaks down and it will need to be replaced. You are just shaking it to see if you can hear fuel in it.