I think Cyril would be a bit creeped out by Constans at first, (but who isn't) partly because he's had less contact with mages and tranquil than the average citizen of Fereldan (spending most of his life in Orzammar and all). After he gets over the 'Huh, you're different' phase though, I think he would quite like him. There's something about being freed from emotions that appeals to Cyril, although he wouldn't want it permanently for himself - more of a thought experiment turned flesh, if you will.
I know Doran/Tech! Although I haven't spoken to her in a while. Cyril is less likely to side with a mage than a fellow warrior, so I don't think that will be a problem.