As usual, everyone is underestimating Wales, and they have their reasons. In the 21st century, Wales has played against Poland six times, and Poland has won all six times. However, we shouldn't underestimate Wales; they are a talented and spirited team. So, the upcoming games will be tough, with both teams at a similar level. Still, Poland has the advantage, and I'll bet on Poland favor.
You already know the answer, met six times and Poland has won all the match. 
Wales is evaluate as strong team because they're from Great Britain, they're overrated. Most of their players are playing in Championship league or mediocre teams in Premier League, while Polans's players are widely playing in Premier League, Serie A, La Liga in upper middle teams.