You would have to pull the tranny out to properly weld it. Youd never get good penetration that would last and you could never stop the leak long enough to clean the area and weld on it without getting crazy contamination and porosity which would end up failing.
Not to mention if i am right its cast aluminum so you will need a tig that can do A/C or a mig with a spool gun attachment.
I really don't know if it will fix the leak. It is possible to weld, and cheaper than a new trans.
So try it, I guess. That is aluminum, so it's harder to find, I might try JB Weld. Fill/coat the crack, let it dry, then (with more) stick on some kinda plate.