I would opt for Banks or Janssen, both of whom have exceptional control. Of the two, I might go for Janssen, who is apparently more polished (and has given up 2 HR to Banks's 4 this year).

The bullpen has been extended quite a bit, so I don't like the idea of Walker (and the guys that pick him up) being stretched out even more. Marcum (if I'm not mistaken) has been a reliever this year, so he probably isn't stretched out, either. Rosario reportedly had good stuff last time out, but he's been hit-and-miss. Purcey clearly needs more time in the minors to sort out his control issues. Downs has been inconsistent at best.

Taubenheim is the wildcard. He's been very good this year, but apparently has somewhat fringey stuff.

I posted this in the MLU as well.

It looks like Janseen is the guy. He was pulled after three scoreless innings today. He threw only 38 pitches.

I was thinking they would go with Banks because he is already on the 40 man roster.

Funny thing with the Jays is they don't seem to worry too much about the 40 man.  I guess JP doesn't figure the 35-40th guys on the list will help anytime soon (given there are 10 guys ahead of them in the depth chart at least) so you might as well go with the best available. 

Me?  I lean towards using Walker and not doing the roster shuffle.  Let the kids impress more in AAA when all you need them for is one or maybe two starts.

If I had to choose I'd go with Janssen.  Not a great ERA to start the year but he doens't walk people, gets his share of K's, and is able to hold down extra base hits against.

Banks on the other hand gives up a similar number of hits and has good control but seems to throw too many fat pitches.  A surprisingly high number of his hits allowed are for extra bases and he's giving up twice as many homeruns as Janssen.  This definately matters at the major league level where the hitters are generally better and less forgiving of mistakes.

Rosario is pitching well but his sometimes erratic control and questions about how deep into a game he can pitch make me concerned about giving him a major league starting job at the moment.  Long relief, sure.  Otherwise let him work his way up to being up to go 6 or 7 innings rather than 5.