The 36-year-old, who was part of Team GB at London 2012, has yet to achieve the qualifying time of 2:14.
Injuries have meant the Guernsey runner has taken part in just one Marathon since the last Olympic Games.
"To get back to that level of the sport and make another Games would be great to put those injury problems behind me," he told BBC Radio Guernsey.
Both Scott Overall and Callum Hawkins have already obtained the time needed to qualify for Rio, so only need to make the top two in London. Merrien, however, must better his time at the 2015 Berlin Marathon by at least 90 seconds as well as finishing in the top two to make it to the Olympics.
"They don't have to run the time on Sunday, they just need to be in the first two, so that adds a different dynamic to the race," added Merrien, who qualified for London 2012 after initially being rejected for a place in the squad.
"They don't need to chase the time, so it's a little bit different for them than it is for people like myself who are needing to get the qualification time on Sunday as well as being in the the first two.
"It would be as meaningful, if not more meaningful, this time round just because I've had to overcome a few more problems than last time."
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Lee Merrien says he is targeting a place at this summer's Olympics when he races in Sunday's London Marathon.