How to arrange an invitation letter for research visit in another university (for PhD student)? I'm a first-year PhD student in Communication and Media Science. As part of the study program, I am obliged to visit the university abroad (the best would be in next year). 

There I need to carry out part of my research, but I would also like to be able to participate in classes with other doctoral students and observe the work of the lecturers. I would like to do this (3 months) at universities in Finland and the Netherlands. 

Is this feasible?  Where should I start? I have never taken part in an academic exchange before. Every advice would be appreciated.
In mathematics, in the U.S., since people in Paris are vaguely acquainted with me, some years ago I was asked to be a supervisor for an Ecole Poly undergrad's "senior project", more-or-less. I had spare time-and-energy at the time, and the people asking me were known to me, and certainly gave the impression that they were not just spamming. (The student was very good, and later won a prize for his paper, "back home".)

So I think if you can get your local faculty to contact people who know them, and can recommend you to them, it might work well. (But, sure, sometimes people are already over-committed, as I am currently, so I sadly had to decline a similar offer, although I knew it would have been quite fun... Just not enough time.)