I can certainly try.
Allocation order is determined by how terrible a team was over the previous season. Officially the league states "The allocations will be ranked in reverse order of finish for the 2011 season, taking playoff performance into account."
Expansion teams always come first, follow by the worst regular season team from the previous year, up through everyone who didn't make the playoffs, then the wild card loser, the conference semi-final losers (worst regular season records first), conference final losers, mls cup loser, mls cup winner. So this year, Montreal is first, and LA is last.
Now this order applies both for any drafts the league does (Superdraft, supplemental draft, waiver draft, re-entry draft) as well as "the allocation process". The way the allocation process works is that whenever a player who triggers the process comes in (again: anyone capped for the USMNT, or any former MLS player who got a transfer fee when they left), there's a conference call. They ask the team at the top of the order if they want the player or not - if they do, the call ends, otherwise they move down the order until someone takes the player.
The cost of taking a player is that you then move to the bottom of the allocation order. So when Eddie Johnson came back a few weeks ago, they had the first allocation process call of the year, and Montreal took him (and promptly flipped him to Seattle). Montreal is now at the BOTTOM of the allocation order - they would have dibs after LA, should a player drop that far.
While the process is an attempt to be equitable for talent, it's mostly broken. Most teams high in the order will grab players and promptly flip them to the teams that want them for money or draft picks or other players (again, see the Johnson trade). There aren't enough incoming players in the span of a year to make passing on a player necessarily a smart move. I think there were 4 last year.
EVEN MORE CONFUSINGLY, sometimes a player will sign with the league and rather than go through this process, they go through a weighted lottery. But that process isn't so well documented.