Liz and Jim McDonald are "never boring"
In August, Lawson confirmed that he would reprise his role in the ITV soap later this year and feature in the 50th anniversary episodes.
Speaking to Digital Spy, he said: "[The romance has] been going on since 1989, so you'll have to keep watching."
Callard added: "It's never boring, that's for sure!"
When asked about Liz's relationship with Owen Armstrong, played by Ian Puleston-Davies, Callard admitted that the Rovers Return landlady can be "so stupid".
"Liz thinks he's great," she said. "But of course the viewers know different. They're just beginning to see another side of him. Liz is completely unaware of that. She's so stupid sometimes!"
Press reports have suggested that Owen could be behind an attack on Jim.
"Liz still loves Jim as well you see, that's the biggest thing," Callard added.
Lawson quipped: "She gets to deal with a man then."