Sorry I can't give you any recommendations. I wasn't in Nagoya for long, didn't do any prior research and failed miserably in my attempt to eat something half decent.

But, to be fair to Nagoya, the main reason we didn't find anything was that after ditching my parents and sending them on to Okayama we didn't emerge from our hotel until after 11pm (our rate included some free cocktails). We walked for nearly an hour and only found a Sports Izakaya with lacklustre food amongst the endless pachinko parlours.

So my tip is don't leave it too late.

Also, although you can find udon noodles almost everywhere, Nagoya has no real reputation for them (EDIT - apart fom udon in a thick miso broth - I forgot!). It does have a fine reputation for soba noodles, but in many places soba and udon are sold alongside one another as they can often share the same broths and soup bases.
Without knowing a great soba shop in Nagoya, and if your concierge can't help you (you want freshly milled, hand rolled and cut soba) my own instinct would be to head to Osu Kannon Temple - there will be plenty of restaurants around this temple specialising in traditional fare.

If you're not to concerned with how splendid your udon is, you could do a lot worse than your local branch of the Udon chain Hanamaru Udon.

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I can give you a restaurant recommendation for Udon in Tokyo
www.setouchi-shunsaikan.com/contents/
Which is run by the Kagawa and Ehime Prefectural governments as a showcase for sanuki udon.

Otherwise, consider popping over to Shikoku and eating udon there. There's a world of difference between the 'normal' soba served at thousands of restaurants across Japan and great soba prepared by a master soba chef. I imagine it's not so different from udon.

One tip for you though, if you do order a bowl of soba or udon with crispy tenpura on the side, be sure to immerse at least one of the tenpura pieces into the soup. The oil is released from the batter and this enriches the broth making it into a more satisfying experience. (This came from a discussion with a very competent udon chef in yanaka, Tokyo who believes that it's the little pearls of melted fat that lie on a broth that do the most to bring out its flavour)

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you've been given an excellent rundown on breakfast choices. I can't comment as breakfast was included with my rate at the Sofitel and I prefer eating Japanese breakfasts anyway. No cheese at the Sofitel, western buffet there only recommended for people who enjoy meat, lots and lots of meat. I'd imagine that the Marriott would fulfill your requirements and then some for breakfast.

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If you are stuck at lunch or dinner times, just go to the department stores around the station. Go down if you want to pick up a bento box in the food departments, or aim for the restaurant franchises they'll have in a slightly different part of the building. You're almost assured of a decent meal there at a good price. If there's a queue - for something that doesn't involve coldstone creamery or krispy kremes - join it. I've never been disappointed when joining a queue for a mystery lunch or dinner.