The Portuguese didn't have a port in Brazil until 1500, and only established sub-equatorial African forts in the 1480s. This scenario would need to have Asian traders establishing those forts instead of the Portuguese. This in turn requires a Japanese presence in the Indian Ocean pepper trade of the 15th century - perhaps off the back of the Chinese presence there.
To my mind Persia is the most plausible one. In fact in OTL there were Venetian diplomats Caterino Zeno, Ambrogio Contarini, and Giosafat Barbaro in Persia in the 1470s, right at the time when their fellow Italians like Columbus and Cabot were pitching royal courts for exploration capital. The Italian diplomats were in a position to have pitched the idea to the Persians too, who already had a base way down in Zanzibar.
Persia's not a bad idea but they would probably prefer a land route, or go through Russia.
Agreed with you but the other one is so much more difficult, it's a fun challenge ;DAs said in a previous post, I think the rise of a colonial Japan is more plausible around 1700 with Holland in decline. Another entry point is after 1602 Ricci and Li Zhizao co-publish the first world map in Chinese, the Kunyu Wanguo Quantu which greatly expanded both Chinese and Japanese knowledge of global geography, just when Portugal is in decline.
For the early version, wattabout this:
Portuguese do arrive in 1498, bloodshed ensues, driving the Muslim out, at least damaging them by 1510. However due to civil war/economic crisis/succession crisis/etc... Portugal stops sending people as a state led enterprise and private merchants get wiped out by slightly miffed Indian princes
In the chaos, the Japanese hear about it, they hear about the high margin possible in Europe and they see an opportunity.
Given they're not muslim, or hindus, or christian, it's very easy for them to talk to everyone. They get a strong presence in the country trade with Chinese imitations, smuggled tea, copper... and from there, try to go to Europe
Because of shenanigans, the Portuguese believe they're christian and do not try to wipe them out but rather send an embassy and founders to help them fight the islamic menace.