Former Peterborough United and Ipswich Town forward Taylor has been training with the club for much of this month - a spell which was interrupted by a groin injury.
And ex-Leeds United youngster Vieira joined up with the Rovers squad last week.
Both men scored in Wednesday night's friendly at Deeping Rangers and McCann says he will inform them in the next few days whether he intends to offer them a contract.
"We'll have a chat over the next two or three days and we'll try to make a decision over them," McCann said.
"They've fitted right into the group.
"Tayls has been here for a couple of weeks, Romario has been here for ten days and they've fitted in.
"They've taken to everything we've spoken about really well.
"They've adapted into the formation and the way we've played so I'm pleased."
Taylor - who played alongside and worked under McCann at Peterborough - has been without a club since leaving Bradford City in April.
Vieira - who played alongside Alfie Beestin at Tadcaster Albion - was released by Leeds at the end of last season. The 20-year-old featured off the bench for Rovers at Grimsby Town on Tuesday before doing the same at Deeping 24 hours later.
"I was pleased with them both on Wednesday," McCann said.
"Taylor looked sharper. He's trained the last three of four days so it was good to get him 60 minutes.
"You could see some of the glimpses of quality, the way he can drift past people.
"He's still way off fitness-wise. He'll tell you that.
"He's getting closer than when he first came to us.
"Romario in the two games has been excellent.
"For a young lad, the composure and his ability to take care of the ball. The lads have really taken to him for that and also the aggression you need in that defensive midfield role at times.
"Both of them have not done themselves any harm and I'm really, really delighted with them."