Everton's need for a new goalkeeper has been increased due to a long-term injury to Tim Howard.
At the moment Roberto Martinez's side have Joel Robles in reserve, but there is a feeling that he isn't ready to play regular Premier League football.
Everton cannot afford to take any risks with their team selection due to their poor form over the opening half of the season and they are now looking to bring in a more secure net-minder to cover for Howard's absence.
McCarthy would likely be the cheaper option of the pair of targets as he is not currently playing first-team football.
Although the 25-year-old has largely impressed when picked, Robert Green has kept him out of the team at Loftus Road to date this campaign.
Marshall, meanwhile, has been a key player for Cardiff this season in the Championship. The Scotland international was their stand-out performer during their short lived stay at the top-level and his performances during the previous year have clearly caught the eye of Martinez.
Everton have also offered Serbian goalkeeper Marko Dmitrovic a trial, but he is expected to be a long-term recruitment rather than a player Martinez intends to plunge straight into first-team action.