HaBO: American Historicals with Cross Country Shenanigans

You did it! We figured this one out! It is a truth universally acknowledged (by me for certain) that the Bitchery pretty much knows everything, and really, it's true. Scroll down to see the solution for this HaBO - and many thanks!

This HaBO request comes from Meredith, who is looking for a book she read a long time ago: 

I'm hoping the bitchery can help me find a book I snagged from my aunt's bookshelf. Sometimes I think I dreamed this book up, other times I'm convinced it must be real. Surely someone can figure out what the hell I actually read. 

Naturally, I can't remember the title or author, but here's what I do remember:

I read the book in 2006, but it was probably published before that. It was an American historical, set in 1800-something, which I distinctly remember because the concept seemed so foreign to me (who cares about Manifest Destiny when you can be snubbed by the ton?!). It may have been part of a series, but I'm less certain about that. It also may have been a Christmas-themed novel.

Our heroine was the youngest child in her family, perhaps with all sisters dutifully married off. Heroine was resisting marriage, because of REASONS, mostly revolving around her desire to run / be a part of the family business (???) and possibly because she had red hair and thus had a fiery temper / temperament. (As a side note, just once I'd like to read about a calm, sedate redhead.) The family lived in either New York or Boston, so let's just call it New Boston. There was discussions of brownstones.

The Hero was a business associate of our Heroine's father, possibly due to take over the family company, much to our Heroine's chargin (of course). I'm not sure how or why, but they both end up racing, a la Jules Verne, across the country to California to win some business person's money / cooperation / whatever.

At some point, there's a kind of kerfuffle during the race, somewhere in the middle of the country (Kansas? Nebraska? Nevada? My concept of geography is appalling), and Hero and Heroine have to share a hotel room. Scandal! Naturally, clothes come off and much sex is had.

Then either the Heroine leaves first to try to beat the Hero to California, or the Hero leaves, thinking that he's seduced the Heroine into giving up the race – I'm not really sure. Either way, they leave separately, but both make it to the random business person and … stuff … happens. The Heroine goes back to New Boston all brokenhearted, though I'm not sure why. Then the Hero shows up – in the snow, obviously – and professes his love. 

Any help is much appreciated!

This sounds like a really epic novel. Do you recognize this book?