so was the paraguayan war...but given the tensions, they couldve seen brazil at war with brtiian as a good chance to spark off sooner... besides it wouldve taken a while for the british to get to brazil, and even though they did have a strong navy, britain had a much better one, plus it controled all the trade routes around the area...it wouldnt need to completly surround brazils coat to choke its trade and supply routes
If Brazil have a war with Britain in 1863 (and frankly, the British government must be extremelly stupid to declare a war over "Christie's affair") then it means that there will be no Brazilian intervention in Uruguay. Without it, and assuming that logic works here, Paraguay has no reason to declare a war against Brazil. Of course, it's Lopez we're talking about here, and logic wasn't his forte, but the fact remains that, at that time, Paraguay had more problems to solve with Argentina than with Brazil.