Please help with subpage duplicate content :P

Hello bhw !
So yeaaaaaaaa..

I just opened a B2B subshop to one of my B2C shops.

example:

shop. com <-- was there since the beginning
shop. com/b2b <-- is NEW

both shops are 99% the same. the differences are just some images and mainly the prices/taxes and the checkout process.
in the eyes of google it must look like 100% duplicate content.

i first wanted both shops ranking for different keywords.

example:
shop. com for "online b2c shop"
shop. com/b2b for "online b2b shop"

that worked amazingly well... up until yesterday looks like my new /b2b shop got shot out of the 1000's
Ok, looks like I cant rank them both, which sucks but whatever..

I now want to "de-rank" my b2c shop and rank my new b2b shop instead.. since that one makes like 10 times the money already lol...

so my question is: how do I do this the best way ? i mean without losing too much "serp power" ;p

I still want both urls to be online of course... so no redirection or something like that.

Should i set <link rel="canonical" href="shop. com/b2b"> ? also noinxed,follow on the b2c shop maybe ? no clue really, help me out please