Timbermate grain filler could be used, but I just use a standard domestic filler as it's got a bit more structural integrity for larger gaps. I've got a tube of Ronseal fine surface filler and a similar Pollycell one, and use whichever is handy. Not sure what brands you've got availble local to you. You won't need much though. They don't suffer from any shrink-back when they dry, like Timbermate can, so keep any filled-gap surface level.

You can make either way work, it's still a matter of taking care regardless of which path you take.