I assume you're talking about this Paxos since you've neither tagged nor specified it.
From the linked Wikipedia page,
Each proposal is uniquely numbered for a given Proposer
So, numbers are comparable, and we automatically have a total ordering on the proposals from a given Proposer.
Can each proposer generate a pair independently from disjoint sets as (seq_number, ip_address) ?
Yes, obviously, you described how to do that in the question. If each proposer has a unique IP address, each Proposer can generate an independent set of such pairs.
However, we don't automatically have any way to order proposals from different Proposers. They're just not related, and I have no idea which precedes the other: this is identical to Jörg's example of the descendant-of relationship in humans. Currently, this is a partial ordering, because we can only order those parts (of the set of all proposals) which came from the same Proposer.
and if we can how can we maintain total order in this case?
By using the IP address in your comparison. You know it's an integer, right? You can just use the normal tuple ordering.
That is, if you want your ordering to be total, you need some way of deciding whether proposal #37 from Proposer A came before or after proposal #42 from Proposer B.
Also can we not maintain a total order by simply generating a (seq_number) instead of (seq_number, ip_address) by multiple proposers?
Only if you don't care which Proposer an element comes from. Your title asks about maintaining a total order among Proposers, and the body of your question is about maintaining a total order among their proposals. You definitely can't order Proposers by just sequence number, because it's only a property of their proposals.