Very interesting question! I suppose the most obvious symmetry that we can identify between these two characters lies in the way that both have a specific goal and they try to achieve this goal through going on an epic adventure. Santiago is of course trying to salvage his reputation by catching a big fish after having had a period of catching nothing whatsoever, and Odysseus is trying to reach his beloved Penelope after being away from her for so long during the Trojan Wars. Both pursue their goal with absolute commitment and resolution, though perhaps we could argue the perseverance and resolution that Santiago shows is greater than that of Odysseus.
However, although we can identify this central parallel, we can also see there are many differences between the two protagonists of these works. Firstly, Odysseus is famed for his skills of deception, which of course Santiago does not share. Santiago is an honest, scrupulous individual who is true to himself and to others, whereas Odysseus seems to be a character who is in love with deception for its own ends. Likewise Odysseus seems to have times in his journey when he suffers from absolute arrogance, which results in him losing lots of his men. Santiago is never arrogant and he journeys alone. We are impressed by Santiago's dignity, whereas at times Odysseus appears to be nothing more than a loudmouth.