Canned Jalapeno peppers and fresh Jalapeno peppers are both pretty hot but in my opinion when I eat canned Jalapeno peppers they tend to be a bit less spicy and hot for some reason.
The fresh Jalapeno Peppers I grow in my garden tend to be hotter than the canned peppers.
But as Jalapeno peppers age they get hotter too.
Maybe it's just me and my tastes but Canned Jalapenos are less hot and spicy to me than the fresh ones but when I grow Jalapeno peppers they get even hotter than the canned Jalapeno peppers do as they age.
Maybe it's a cooking process or something with the canned Jalapenos that make the canned Jalapenos less hot or something they put in it to remove most of the Capaiscin from the Jalapeno pepper which is the chemical that makes hot peppers in the Capiscum family taste 'hot'.