In an interview with RDS, David Perron spoke about his free agency decision back in July. He says that when it came down to making the decision, the Montreal Canadiens were one of two teams he was considering signing with. The only issue was the dollar amount of the two contracts he was offered.
According to Perron, his first choice was to return to Anaheim, but when that didn't happen it was between Montreal and the St. Louis Blues. He says that he would have been leaving a lot of money on the table if he chose the Canadiens, so he landed on St. Louis.
The following is a quick quote from the video, translated from French.
"My heart was talking a lot, and it came close. There would have been a lot of money left on the table, and I couldn't really take that chance, so it was for that I chose St. Louis."
You can't really blame him here. At his age he only has so many years left to cash in on his abilities, and Montreal was probably trying to get him on some sort of hometown discount. Hard to fault him for taking the money and going to a team that is considered to be quite the threat in the West.
Considering he signed at $3.75 AAV with the Blues, I'd be very interested to know exactly what the Habs had offered him. In any case, it wasn't enough, but they were definitely in the mix all the way down to the wire.