Tuifua recently linked up with Blues from Taranaki and the big-hitting Samoa international could now be unleashed after being named on the bench as the region looks to finish the cup competition on a high and build momentum before a return to league action.
Tom Williams switches to full back with Dan Fish named on the wing. Richard Smith is recalled to the opposite flank.
Fit again fly half Gareth Davies will partner Lewis Jones at half back and Gavin Evans will play at inside centre alongside Wales international Owen Williams.
Filo Paulo makes is back in the second row while Macauley Cook returns at blindside flanker.
Back row Robin Copeland is released back to Blues from Ireland and takes his place among the replacements.
“All of our players are looking forward to the game as it’s another great opportunity for our young team to show just what they are capable of,” said Director of Rugby Phil Davies.
“We have a number of injuries, but this is the strongest team we can send out. We will be giving it everything to secure a big result and build momentum before our return to league action next week.
“Harlequins are one of the teams in the Premiership that I admire most,” he added.
“They have developed a fantastic brand of rugby with a strong set piece backed up by an attacking game full of speed and tempo.
“They’ve worked exceptionally hard to become one of the top sides in European rugby, have been ultra-consistent and boast a very powerful squad. We have a big challenge ahead of us, but it is one we are relishing.”
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Cardiff Blues: 15 Tom Williams, 14 Richard Smith, 13 Owen Williams, 12 Gavin Evans, 11 Dan Fish, 10 Gareth Davies, 9 Lewis Jones; 1 Thomas Davies, 2 Rhys Williams, 3 Benoit Bourrust, 4 James Down, 5 Filo Paulo, 6 Macauley Cook, 7 Ellis Jenkins (c), 8 Luke Hamilton
Replacements: 16 Marc Breeze, 17 Sam Hobbs, 18 Scott Andrews, 19 Chris Dicomidis, 20 Robin Copeland, 21 Lloyd Williams, 22 Simon Humberstone, 23 Isaia Tuifua