Minecraft villager

As long as you haven't bought anything from them, meaning their experience bar is 0, you can switch a villagers profession by creating a workstation for a different profession, and then tearing down the workstation they had. Make sure there are no other open workstations of the cartography profession available for them to use.

As long as they have not gained experience or levels, they will eventually give up the profession and switch. Now do the same thing again but instead of any other workstation, put back the cartography station and they will become a cartographer again and the things you can buy from them will be rerolled.

Bear in mind, you can essentially only roll their first tier purchases so even if you max the second cartographer after trolling, there is still a chance that all the later purchase tiers might be the same.

Also, once a villager gains experience with a profession, its locked and cant be changed with the above method.

From villager minecraft wiki:

A job site block can be claimed only if it is unclaimed and within a village boundary with at least 1 bed. Removal of a claimed job site block causes the owner to switch to another profession or become unemployed, provided that the villager has no prior trades with the player. If the villager has prior trades, it keeps its profession and claims a new job site block that matches its profession if one is available. So, once a player trades with a villager, the villager keeps its profession forever.

Assuming you actually want a second cartographer, to get more cartography trade options:

Have you levelled up your second cartographer?

Take a look at the table of cartographer trades. The cartographer will pick two additional trades with each level it gains, from one to five, to a maximum of 10 trades. Each trade option it makes has a minimum level requirement.

As a novice cartographer (the new cartographer) has only two trades available to it, it will always offer those two trades.

An apprentice has only four options available to it, so again always has the same offers. Journeymen only have six, so again the options will be fixed.

But, once a cartographer becomes an Expert or master, it will give you four more options out of 17,17,18,18. That means it has 17 * 16 * 16 * 15 = 65,280 choices. In other words, there are 65,280 unique cartographers out there.

But if you did already level it...

You may have had some really bad luck?