I have been canning starters for a couple years now. I usually use maris otter for the starter since that is my usual base grain. I use this for all styles. I keep a bag of pilsner malt around that would also work, but because of the closed boil in the canner, the dms precursors really can't be boiled off. I don't use pils malt for starters for that reason. I don't want to get any of that into my finished beer.
I prefer to boil the starter wort for 15-20 minutes before putting into the jars to minimize the hot break in the jars, though it doesn't really make any difference. There is the added advantage of being able to bring the temperature of the pressure canner up a little quicker if you start with hot starter in the jars.
Wayne
