I was charged with theft under 5000 but I went through the alternative measures program so I was never convicted or fingerprinted. But it will show up on my record (in Canada) for a year. Seeing as Ive never been convicted or fingerprinted will the US border still be able to see my record, and if they do what's the worse thing that could happen? I'm planing to go to the states with my friends and I don't want there to be any problems

It is possible you will be stopped at the Border and not allowed entry.

Yes, your arrest and the disposition will be visible to Homeland Security IF someone checks.