How to import OpenCV android-sdk to my project which is using Bazel?

I see that there's an opencv-android artifact on Maven.

You can depend on this using rules_jvm_external.

In your WORKSPACE file, specify the dependency along with the other external dependencies:

load("@rules_jvm_external//:defs.bzl", "maven_install")

maven_install(
    artifacts = [
        "org.opencv:opencv-android:1.0.1",
        # ...
    ],
    repositories = [
        "https://maven.google.com",
        "https://jcenter.bintray.com",
    ],
)

Then, in your BUILD file containing your Android targets, depend on the OpenCV target:

android_library(
     name = "my_lib",
     custom_package = "com.example.bazel",
     srcs = glob(["java/com/example/bazel/*.java"]),
     manifest = "java/AndroidManifest.xml",
     resource_files = glob(["res/**"]),
     deps = [
         "@maven//:org_opencv_opencv_android",
     ],
     visibility = ["//src/test:__subpackages__"]
)

Finally, you should be able to reference classes like org.opencv.core.Core in your Android Java code.

P.S. consider switching all your maven_jar and gmaven_rules/gmaven_artifact to use rules_jvm_external. The former Maven rules have been deprecated in favor of rules_jvm_external.