Need help with Canonicals and Duplicate Content!

I am working for a client that is operating in the DACH region ( DE, AT, and CH). They have three separate websites not a single .com. They would like to take their German Blog content for DE, put it on the blogs for CH and AT. I told them is not a good idea but still they insist on it. Will implementing proper canonicals pointing to master copy on the .DE domain allow to avoid duplicate content issues?