If you want to RP as a straight male, though (the only reason I ever do this is literally for Morrigan), I honestly think either Morrigan or Leliana could work depending on how your character turns out. Morrigan is intensely practical, and this could work for a cynical dwarf. I think your dwarf's "ignorant of everything" problem could be worked around depending on how secure/insecure they are about asking questions; a more proud character, or a character who is trying to keep the illusion of composure to stop them from breaking down, may stay tight-lipped and try and hide the fact that at the back of their mind is a voice wondering what the hell is wrong with these mages why are they mutating into flesh-eating monsters and abodinations and does that usually happen. I also think dwarf's relationship with magic affects your chances with her: if your warden is suspicious of magic, then I'd be disinclined to pick Morrigan, who would likely be dismissive of your attitude no matter how sensible and practical it is from a dwarf commoner's point of view. Morrigan has had a similarly sheltered upbringing as the warden - that could be a plus or a minus, depending on how judgemental she's feeling and how your character reacts to that.
He starts off perfectly okay with all types of magic, not seeing any problems with Morrigan's shape shifting for instance. They don't have ANY programming or propaganda from the Chantry that makes them distrust and dislike magic. Yet... They actually become more anti-magic over the course of the game, as magic related problems continue to pile up. Soldier's Peak's problem? A mage's fault. Redcliffe's problems? A mages fault. Circle tower problems? A mage's fault. Werewolf problem? A mage's fault. The only treaty quest that was messed up that wasn't caused by a mage was only the dwarven one, because of the obvious "dwarves can't use magic" thing. 3 out of 4 treaties issues that needed dealt with was magic and a mage's fault, and the only one that wasn't probably only wasn't because it was impossible anyway. So even without any Chantry teaching, they start to get very very irritated about how massive of problems magic can cause and how damned frequently it seems to be happening.
So they start pro-mage and pro-magic at first because they're practical and see usefulness in it, and become a lot more neutral-to-negative about it as more and more mage caused problems keeping getting in the way of obtaining allies with the treaties. Interestingly, the responses he gives to her magic questions that will get approval from her will happen earlier in the game before he starts veering to a more anti-magic view. So it's kinda weird, if he had the same views early game that he does in late game they might not have liked each other. Not to say he
hates magic and mages, but he can see why people distrust it. Sort of. He blames human-dwarven-elven fallibility mostly, but realizes that the fallible traits we have can be so much worse if they have magic at their disposal on top of it. So individual mages who have a good head on their shoulders like Morrigan and Wynne, he doesn't mind. But he also realizes that magic itself is a cluster f*** and is ultimately glad his people can't use it, because he knows his people well enough to know that dwarves would have already destroyed their own society if dwarves were able to toss fireballs and merge with demons easily. Seriously, take dwarven culture and add magic... Utter chaos.
Summed up: starts completely okay with magic, ends wary of it after a strong pattern emerges of stupid mages causing nightmarish scenarios. He doesn't mind magic traditions or rituals like Morrigan's late-game one and doesn't mind mage allies, but does realize that mages and stupidity are a
VERY BAD combination. Smart mages=awesome allies who are absolutely trustworthy, stupid mages=potential disasters.
Leliana could also work - I think for more open characters she'd be a more natural option, especially when hardened. She's much more relaxed about the warden's choices, as long as they aren't completely heineous and/or blasphemous, and won't call them a fool for throwing a raggedy old beggar a silver or two. Leliana has also the added bonus having travelled the world and seen different countries and places and cities: the warden hasn't, and that might be part of the allure - she's everything Orzammar isn't. She definitely lines up with the attitude of having seen and understood some of the more terrible parts of the world (she once had a pretty cut-throat attitude as a bard), but endeavouring to find and nuture the good in it despite that. Definitely more world-weary, although the initial 'cloistered Chantry nun' impression may put your character off. In terms of potential issues, if your dwarf is more closed off or cynical, your drawf might find her dreamy stories and pleasant chatter rather irritating than a light relief.
You see my problem, both can work very well with a casteless which makes deciding that much more difficult.