I thought Gt3 sold was released a year after the ps2 release. If I'm not mistaken, the Ps2 at that time had a lower install base than the Ps3 today (well, this fall).
GT5 also has no competition this fall ( I think), but it seems like there's going to be a ton shooters coming out this fall. Also: sequels tend to sell less than their predecessors on the same consoles. However halo 2 outsold halo 1, so anything could happen.
Every gt game has sold at least 10 mil except for gt2 which sold 9.3 mil. However this game was released in the year 99/00 right before the gt3 & Ps2 came out which cold have prevented it from hitting 10 mil. I think GT4 could have sold slightly more if the 360 wasn't released shortly after it released. With GT5 being the Ps3's first gt and no new consoles or gts coming out anytime soon, I think it should outsell Halo.
The best selling halo ( halo 3) was released when everyone needed a halo to play. Also The Ps3 was basically a joke a that time. The 360 was the more popular console. Today, however, the ps3 has gathered momentum is more popular in most countries and people need a GT game. With halo: odst just released last year, I think a lot of people may think halo: reach will be a very short game . I know odst wasn't a real game but be honest, most gamers are uninformed. Most of them don't read gaming news, read gaming magazines, or stuff like that. A lot of gamers make their decision based on what they see when they watch commercials and when they see the box arts. A lot of them won's see a number in the title and they won't think it's a full game. Halo will sell good but I doubt it'll outsell gt5. I'm 70 % sure it won't. : ). I'll be buying both, but if I had to choose one, i'll choose GT5 with no regret
A large portion of sales also depends on marketing and stuff like that.
