Can a 20' 6x12 rdwood be safely supported by 2 redwood knee-braces at each end 17'apart?

Question:This is for an arbor over a 16' garage door. The house is stucco'd and there's 5 1/2" of foam trim around the door, so the closest I can get the corbels mounted is at 17'. They're 6x10 or 6x12 corbels. They're bulged at the bottom and end to end they're 31.5" with about 7" of landing at the wall end as well as at the top. If this is possible, can these simply be lagged-in thru the stucco and into the wall? I think there's 6x's in therenext to the kings. There will be a 2x12(20')ledger lagged into the gar. header and 24" long 4x4s laying across the top at 16-20 in. on center. Any help guys, please and thanks.. Is 7" 3/8 lag-screws enough? Maybe little clips on the side? It just doesnt seem like this will work. I'm not so much worried about sag as much as I'm worried that the knee-braces will just snap with that much weight.

Answers:
hello again ... since you are adamant about not removing the stucco to properly attach the arbor to the framing i suggest
"Simpson" type metal brackets that can be lagged thru the wall then place the braces in the brackets and lag the brackets into the braces The size of the corbels seems sufficient , its just the attachment to the structure that concerns me. Local construction suppliers should be able to help you get the proper hangers