I don't know if it's gauche to put a link to one's blog in a forum, but if anyone is interested, I examine Alistair's marital prospects as sole ruler of Ferelden as of 9:31 Dragon in some detail (just scroll down to the footnote). It's pretty long, so I won't post all of it here. But, if you want a preview, here's part of it (SPOILERS):
Marrying outside of Ferelden:
In order to be acceptable to the Landsmeet, his potential wife would have to possess similar values. This immediately excludes Tevinter. Because magic is still regarded with suspicion in Ferelden, a mage wife, much less one from a country which espouses slavery, would be out of the question. A wife from Rivain, being non-Andrastian, also would cast suspicion upon the throne, let alone a wife from Par Vollen or the Qunari-controlled Seheron. Choosing a wife from among the warring plutocrats of Antiva would risk incurring the wrath of rival houses and the inevitable attentions of the Antivan Crows.
There are also logistical issues, such as the availability of an appropriately aged, unmarried female who would be willing to marry Alistair. Given the ruling dynasty of Pentaghasts is dying out, this eliminates Nevarra as a possibility, at least, until a new dynasty takes over. While the King of the Anderfels holds power equivalent to a Fereldan Teryn or Orlesian baron, it is unknown whether he has any daughters or sisters. Besides, with the Wardens largely governing the Anderfels outside of the capital and Alistair already being a Grey Warden, it would be difficult to see what further political or economic advantage could be gained through marriage. Other options include a noblewoman from the Free Marches, and of course, Empress Celene. Of the latter two, forming an alliance with one of the three most powerful families in the Free Marches appears the most viable and attractive option, as it might result in improved agricultural trade, something the Blighted lands of Ferelden would sorely need. Unfortunately, neither Prince Goran Vael of Starkhaven nor Viscount Marlowe Dumar of Kirkwall have marriageable relatives, while little is known of the Teryn of Ostwick. The benefit of an alliance with Orlais is less clear-cut. As evidenced by Loghain's ability to gather allies to his cause, residual distrust of Orlais in the Landsmeet is not something to be underestimated, particularly now that the Blight is no longer a pressing issue. Given the 27-year-old Celene's lukewarm response to Cailan's proposal and rumours of her unhappiness at having her chevaliers turned away at the border by Loghain, it is unclear whether she would now consider such a union, particularly to a country weakened by the Blight.