About 3 years ago, when I was finishing my Master's, I applied for a PhD position in a Canadian university. Everything went well and the professor provided a letter of reference to the members of admission committee indicating his acceptance to be my supervisor and fully fund my research (he sent me the letter to submit along my documents).
But unfortunately due to some personal circumstances I couldn't continue my studies and attend the PhD position.
Now, I am again considering applying for PhD (in some other universities) and was wondering: Can I use this letter of reference as a kind-of letter of recommendation? If so, should I ask his permission?