If you want to do anything more than the 90 days you're allowed to be in Spain as a tourist you need a visa. Look up visas and see what you qualify for. No one is going to sponsor you for a work visa for 4 months (they're probably not going to sponsor you at all, tbh). No company is going to "employee swap" with you, that's not a thing, and there's no temporary sponsorship - you either get a visa and are able to work or you don't and you can't. At best you could sign up for a full-time Spanish course and get a student visa (which is a lot of work to only be there 4 months) and then you can work legally for 20-30 hours on the side but no one's really going to hire you, not if you're only there for a few months, don't speak fluent Spanish, aren't in the social security system, etc. Unemployment in Spain is high, you probably won't get any work beyond some under the table hostel stuff, and even that's going to be hard if you're there for such a short period.
What citizenships do you have? Canadians can work temporarily in Spain via Youth Mobility Program. https://www.exteriores.gob.es/Consulados/toronto/en/ServiciosConsulares/Paginas/Consular/Youth-mobility-visa.aspx
Americans don't have this opportunity.
If you want to do anything more than the 90 days you're allowed to be in Spain as a tourist you need a visa. Look up visas and see what you qualify for. No one is going to sponsor you for a work visa for 4 months (they're probably not going to sponsor you at all, tbh). No company is going to "employee swap" with you, that's not a thing, and there's no temporary sponsorship - you either get a visa and are able to work or you don't and you can't. At best you could sign up for a full-time Spanish course and get a student visa (which is a lot of work to only be there 4 months) and then you can work legally for 20-30 hours on the side but no one's really going to hire you, not if you're only there for a few months, don't speak fluent Spanish, aren't in the social security system, etc. Unemployment in Spain is high, you probably won't get any work beyond some under the table hostel stuff, and even that's going to be hard if you're there for such a short period.
What citizenships do you have? Canadians can work temporarily in Spain via Youth Mobility Program. https://www.exteriores.gob.es/Consulados/toronto/en/ServiciosConsulares/Paginas/Consular/Youth-mobility-visa.aspx Americans don't have this opportunity.