no difference in head gasket. just brand and thickness.
never heard of candadian castings. There is navastar castings and Dalton castings, old gm castings and some china crap out there.
Navastar is what you want if they are used. If you buy new from G.E.P. they will be a Dalton cast unless you get the last of the navastar castings they have in stock.
I just went through all this buying my new GEP engine thinking I was getting a navastar and instead I got a Dalton. I have had one issue already with the Dalton heads hopefully I have no more. I am still building the motor so it is not running yet to give any more info.
After all the research I have done, nothing about Canadian castings.
I have put the head gaskets side by side and no difference. There is big difference in quality and thickenss depending on brand. with the turbo and 6.5 heads. I would go with the thickest gasket you can get.
my 2 cents, hope they work for you.
Rich