The outside-back will fly into the UK early next week and meet his new team-mates following a long wait for his visa application to be processed.
The visa came through in the last 24 hours and he’s booked to come into the UK on Monday,” Sheens told the Mail.
“He’s another outside back with some size and he’s got versatility – he’s played wing, centre and back-row on both sides of the field. It gives us some depth and hopefully some more thrust out of our backs. A 100+kg player always helps.”
Though Vaivai is scheduled to arrive in Hull ahead of the Easter period, Rovers are not looking to hand the former Penrith man - cousin of Hollywood actor Dwayne 'The Rock' Johnson - a debut anytime soon.
Instead, Sheens will be patient with Vaivai, who has been keeping in shape via his personal training business back in Australia.
“We’ll assess him when he gets here – we’re not going to push him and risk injury but I’ve been keeping in touch with Junior and I’m fairly happy with the shape he’s in," Sheens added.