In Be'er Hagoleh, Be'er Revii, the Maharal writes:
והדברים אשר נבאר הם דברים אשר נמצא
בספרי חכמה גנוזים וטמונים, על
אותן הדברים לא נוסיף ולא נחסיר
This seems to tell us on what he is basing his Sefer. He often leaves subtle Kabbalistic hints as to what he is referring to. An example can be found in Tiferes Yisroel 55:
והבן הדברים האלו אשר אמרנו כי אין לבאר יותר מזה, אך כאשר תעמיק תמצא כל הדברים מבוארים נמשכים מן החכמה ומגיעין עד הבינה ואל הדעת, ובדרך זה נמשכים אל יסוד אמונה
As to which sources the Maharal utilized, see his introduction to Be'er Chamishi of his Be'er Hagoleh
ותחלה נאמר שהיה להם לתת לב, שנמצא בדבריה׳
איזה ענינים שיראה לאדם רחוק מן הדעת
וסתומים הם במקומם, וסודם נגלה מבואר במקום
אחר כמו במדרש הס׳ הזוהר ובמדרש הבהיר לר׳
נחוניא בן הקנה ושאר ספרי חכמה, אשר הם
גנוזים וכמוסים באוצרות חכמים
We also have him quoting R' Meir ibn Gabbai' Avodas Hakodesh and Maarachos Elokus in Derech Chayim, fifth chapter on the Mishna of the ten things created Erev Shabbos.
Now, the Arizal is not the originator of Kabbalah. The Arizal himself had a Rebbe, the Ramaq, although at some point he surpassed him. The Ramban was famous as a Mekubal and wrote much, although not very explicit. This is even before the Zohar Hakadosh was found. The Ramban had a Rebbe, Reb Ezriel, who learned from the great Ri Sagi Nahar. There are also writings in Kabbalah from Rav Hai Gaon, who mentions the Mesora of the Roshei Yeshiva.
Since the Maharal doesn't discuss Kabbalah openly it is hard to speak of his particular Shita in esoteric topics. But being that he was before the Arizalwe'd naturally assume that his Kabbalah would have been in line with pre-Arizal Kabbalah.
However, in the מגילת יוחסין printed in the first volume of חידושי אגדות מהר"ל, he mentions that the Maharal met the Ri Sarug, who was a much celebrated Talmid of the Arizal and left before Reb Chaim Vittal came. He is the mentor of the Rama MiFano in Toras Ari.
Interestingly, there is one parallel which I found. The Maharal, in discussing the Aggadata in Nidda 24b, about when Abba Shaul describes the depth of Avshalom's eye, explains that before the creation was possible the void for it had to first be created. This very much parallels the concept of צמצום.