As a random aside, I take back what I said the other day about the Templar side being dull. Played through it earlier and - while it was deeply frustrating trying to find everything, loot everything and keep Barris alive - it was far more fun than I initially gave it credit for.
While I'm still going pro-Mage as my canon save, I'm going to do a Templar run alongside this one with the same character, as a nice little "What if?" AU.
And this works in-universe as well, since Alexius has already changed history at least once before we arrive to Redcliffe in the Mage side and in the Dark Future, his diary states that he's made at least ten attempts to go back and alter history in various of ways. One could imagine that in one of these potential timelines, the Inquisitor decided to forego infiltrating Redcliffe castle to instead seek out the Templars help to close the Breach and provide some backup to deal with Alexius afterwards... not counting on the attack on Haven occuring later that night.
(Yeah, I know some people hate the timey-wimey ball in Inquisiton, but I love it)