I will be visiting Spain for Christmas. Any resources regarding tour planning are appreciated.

Where? It’s a big country.

Komoot is awesome for finding routes and rides in Europe

Check out the Eurovelo routes in Spain as well

As romantic as it sounds, basically the whole of the Spanish mediterranean coast is horrible. Massive over-development of tourist infrastructure and agriculture under plastic sheeting, along with heavily traficked roads has ruined it.

Inland and especially in the mountains is a whole different world

edit: I re-read OP’s post. Xmas time… check the weather forecast out! Even in the south it can get cold, wet and windy… as well as warm, dry and sunny

Where in Spain?

+1 on Komoot for Europe.
I cycled in the Costa Brava this Sept and that was not my experience, at all. I was with locals, so maybe that had something to do with it. We hit more than a few Vuelta climbs too, but it seemed like we were off the beaten path. The French Pyranees were a lot busier.
I'm going to Ripoll in the spring for more cycling with my friends, that should be cool.

Barcelona and Seville, to be precise.

Get The Rough Guide to Andalucia and the Micheline map of the territory. Avoid snowy mountainous areas.

I'm considering getting a guide. I was checking https://gowithguide.com/spain Did you use their service? Maybe you can suggest some if you previously used one.

If you hope to get helpful answers, you need to go into a lot more detail about what you want to do as it pertains to bicycle touring. Most of us here plan our own tours.

Backlands of Valencia, Montañas Vacías, Pueblos Blancos, Sierra de Segura y Sierra de Cazorla! Beautiful places ...
If you want some visual input and motivation take a look here: https://www.flickr.com/photos/42743731@N00/albums/
Stay away from the coast. Don't cycle on national roads.

Also, Barcelona and Sevilla are VERY VERY touristy!

Camino de Santiago. 500 miles from St. Jean to Santiago. Earn an Indulgence to heaven.

Thanks for sharing. This little Spain tour is too interesting to me https://www.flickr.com/photos/427437...7720310841375/

It looks very green. I’m guessing it’s the Galicia region in the North-West and the Atlantic coast. Beautiful.
Galicia has a very different climate than the rest of Spain. Lots of rain (that‘s why it‘s so green, duh). Cold, wet and windy in the winter. Not an area to tour at xmas time.

for Christmas I would stay as close to the southern coast as possible or hop to Mallorca / Ibiza

Christmas that will be cold and most probably rainy.

It is south Bilbao - Burgos

Christmas Mallorca is a nice advice.

If you want to go rural mainland this place here has a nice climate, if the weather is stable.

We toured between Malaga and Sevilla among the pueblos blancos (white villages) last October/November. At that time of year, the weather was great - long sleeves in the morning/evening and on descents, short sleeves for much of the day. Beautiful cycling among olive groves and small villages, but best bring your granny gear.

Toured for 7 weeks there in 2000. Mid-March through the end of April. Loop from/to Sevilla, including much of Semana Santa in Ronda. Was grateful for my 24x34 low gear.

I would recommend that you check into the weather. Northern Spain (green Spain) is considerably cooler than southern Spain.

Even areas in the south get cold. I saw snow on the peaks and hills around Ronda and Cazorla in April.