"There's no doubt we've made huge progress over the last few months," said Hadden, whose side came within a single score of upsetting the world champions three months ago.
"It will be an extremely tough challenge for us but we believe we're more than capable of being really competitive against them - and beating them."
Despite heading into their tournament opener without two of their form players in Nathan Hines and Euan Murray, Hadden feels his side now have the kind of quality throughout the squad that will allow them to challenge the very best.
"Wales are the Grand Slam champions and rightly favourites for the championship this year," added Hadden.
"They have a star-studded line-up in both the forwards and backs but crucially, they have hardly had any injuries.
"They have had a settled side for the last couple of years and if we'd been like Wales, we would have made faster progress.
"We had a massive number of injuries in the last two Six Nations campaign and the injury list is mounting again.
"But we believe we've got the strength in depth which makes us competitive."