But Hearn, Liam Underwood, Sean White and Pat Kay were all late arriving, after having taken part in the World Rugby Pacific Challenge in Fiji.
"They are a little bit battered," Middleton said. "They obviously played four (15-man) games in just over 12 days so they are pretty beaten up."
Middleton will only have two sessions with his full roster ahead of Friday's opener against Belgium. The Canadians finish out pool play Saturday against Samoa and Fiji with Sunday reserved for the Cup and other finals.
Douglas, Hearn and Duke missed the U.S. stop on the sevens circuit last month. Douglas and Hearn were injured while Duke was unavailable due to medical school interviews
Canada tied for seventh in Las Vegas, losing 17-0 to Australia in the Plate semifinals. It was the best showing in five events this season, with the Canadians currently 13th in the series standings.
It has not been an ideal start for a number of ways. Middleton, a Zimbabwe native, missed the first event in Australia on the circuit due to immigration red tape and only now is putting his stamp on the program.
"I think we're just looking to build on some of our performances," said Middleton. "The first two (events under his helm) in Dubai and South Africa were difficult for me just in terms I had only arrived a few days earlier. So that was every observational.
"Then Wellington (New Zealand) and Vegas were about making some strides forward with our game. I felt we did that objectively. It's not always to assign results to it although I understand we're a results-based business."
Unlike some of the sport's top countries, Canada shares its talent pool between the seven- and 15-man game. So Middleton has had "very limited" preparation time with his players since the U.S. sevens stop.
"But we've identified some aspects of our game that we just want to make some inches forward in."
For Middleton, that's improving the efficiency of the Canadian attack and "robustness" in defence.
Assistant coach Kieran Crowley, who coaches the 15-man senior team, and physiotherapist Danielle Mah also made the trip from Fiji to Hong Kong.
Admir Cejvanovic, Burnaby Lake RFC, Vancouver; Mike Scholz, Castaway Wanderers; Oakville, Ont.; Mike Fuailefau, Castaway Wanderers, Victoria; Justin Douglas, Abbotsford RFC, Abbotsford, B.C.; Lucas Hammond, Toronto Nomads, Toronto; Harry Jones, Capilano RFC, North Vancouver; Ciaran Hearn, Castaway Wanderers, Conception Bay South, N.L.; Pat Kay, UVIC Vikes, Duncan, B.C.; John Moonlight (capt.), James Bay AA, Pickering, Ont.; Conor Trainor, UBCOB Ravens, Vancouver; Liam Underwood, Ontario Blues, Toronto; Sean Duke, UVIC Vikes, Vancouver; Sean White, James Bay AA, Victoria; Adam Zaruba, Capilano RFC, Vancouver.
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