The NASA B-57s are heavily modified Canberras and I believe still in occasional use. I would guess they have or still do use the U-2 as well. The Canberra was ahead of it's time and a record breaking aircraft - when one was first flown to the USA the USAF tried to intercept it with their latest state of the art fighter the F-86 Sabre - and the Sabres could get nowhere near the Canberra as if flew far higher than they could reach.
In terms of "book numbers" the US sabre has a slightly higher maximum ceiling but if the Canberra was already at 48,000 feet and the Sabre was trying to intercept it would take an awful long time to get up there, the Canberra would be long gone.
The Aussie CAC/Avon Sabre variant would have more chance. It had a Rolls-Royce Avon R.A.7 with double the thrust of the General Electric J47 fitted to US variants resulting in a 3000' higher ceiling. It also had more fuel allowing a longer tail chase and was fitted with a pair of 30mm Aden revolving autocannon with 1000+ / minute ROF, instead of the 0.50 cal of the F86.