Marner, who turned 22 on May 5, had NHL career highs in goals (26), assists (68), points (94) and rating (plus-22) in 82 games last season.
"Obviously, he's a huge part of what we do in every regard and we're hopeful he's going to be a Leaf for a very, very long time," Dubas said. "So we'll just keep working away at it and see what happens."
The Athletic reported that Marner may be seeking a contract similar to the one teammate Auston Matthews signed in February (five years, $11.6 million per season). The website said Toronto may want to offer a three-year, six-year or seven-year deal, with the term in part designed to avoid conflicts with other contracts when they come to an end.
"Hopefully as the calendar begins to turn, we can begin to get it towards a spot where he's ready to go for training camp," Dubas said. "I mean, we were sure hopeful to have it done in the spring, unfortunately we weren't able to do that, and so we'll just keep working at it, working with (agent) Darren Ferris and working with Mitch. …
"I'm confident. I'm optimistic, so I'll stay that way until the end."