Sorry, 7 weeks is WAY too short for what you want to do. If you head south, circle around east, then north and come back west, there are only a few routes without back-tracking or going thru Columbia....
From Brazil you can:
(1) turn back west at Porto Velho and all the way to Cuzco
(2) catch the boat out of Porto Velho to Manaus, then west to Iquitos (Peru), and up river to Yurimaguas. Then take the road to Tarapoto and west to Jaen, then north up into Ecuador
(3) ..... from Iquitos up the Napo river until you get to a road in Ecuador, then over to Quito (This is a long, roughing it, river ride, but do-able)
But back to the time: South America is huge! Calculate no more than 600 kms a day on pavement, and no more than 400 kms a day on gravel (unless it rains, then count on only 25 miles in a day!) Count on one day at each border crossing... If you get any kms covered that day, count it as a bonus, not a given. Ride 2 days, then a day break to work on the bike and BREATHE!
Even the small loop, barely dipping into Argentina, you are talking 3 months! See my blog and see what we barely could do in 7 weeks starting and ending in Peru...